1. Field of the Invention
The present invention relates to an on-screen display (OSD) circuit of an imaging system. More particularly, the present invention relates to an on-screen display circuit having a simplified configuration.
2. Description of the Prior Art
Conventionally, in the imaging system such as camcorder, television receiver, monitor and the like, there is provided with an OSD function to display on a screen the numerals or the characters that represent a selected channel number, the time and date, the information for guiding a user, etc.
Generally, the imaging system produces a vertical edge compensation signal and a horizontal edge compensation signal. The vertical edge compensation signal changes an amplitude of luminance signal in accordance with the amplitude of black signal, in order to perform the OSD function that represents The characters or the numerals on the image display device.
FIG. 1 is a block diagram of a conventional OSD circuit applied to the imaging system.
As can see from FIG. 1, a luminance signal Y is inputted to a vertical edge compensation signal generating part 21, a horizontal edge compensation signal generating part 14 and an adder 16. Adder 16 sums the luminance signal Y, the vertical edge compensation signal from vertical edge compensation signal generating part 21, and the horizontal edge compensation signal from horizontal edge compensation generating part 14 and then outputs a first luminance signal to a gain amplifier 17. In gain amplifier 17, the first luminance signal is amplified to have a desired gain value and the amplified first luminance signal is inputted to first switching part 23.
When an OSD controller 10 does not receive an OSD control signal from a user, it controls a first and a second switching parts 22 and 23 so that the first luminance signal amplified in gain amplifier 17 may pass to reach a display device (not shown). However, when OSD controller 10 receives the OSD signal from the user, it supplies a blanking pulse and an OSD blanking signal to first switching part 23, and supplies a data pulse and an OSD data signal to second switching part 24. In first switching part 23, the amplified first luminance signal from gain amplifier 17 is blanked in accordance with the OSD blanking signal to define a blank leveled area of a display device for realizing the OSD function, thereby producing a blank luminance signal, which is inputted to second switching part 24. In second switching part 24 which receives the blank luminance signal, a blank leveled area defined by the blank luminance signal receives the OSD data signal thereby to produce a luminance-OSD signal which is inputted to the display device.
However, in the OSD circuit as described above, it is necessary to provide an OSD controlling circuit 29 including first and second switching parts 23 and 24 and OSD controlling part 22, for controlling the OSD blanking signal and the OSD data signal. Generally, the OSD circuit shown in FIG. 1 is formed on a single semiconductor chip. However, when the OSD circuit has the above switching parts, an additional element for driving the switching parts and thus the OSD circuit configuration becomes more complicated, thereby increasing the manufacturing cost. Therefore, it is preferable to eliminate the switching parts.